There are a number of applications in which chemical components in a mixture need to be separated. The fields of application include many industries such as chemical, environmental, food, medical, enzymatic, pharmaceutical and recycling. The problems to be overcome by the present invention will now be discussed with reference to the recycling industry, but it should be understood this discussion is representative of the problems faced by the other industries.
Used lubricating and hydraulic oils are generated by a number of industries, including automotive and commercial shops, large industrial manufacturing facilities, marine facilities and airline and railroad maintenance departments. Used oils are considered hazardous wastes and are heavily regulated. It is the contamination of these oils with water and waste products that prevent their continued use. Generators of used oils are responsible for cradle to grave management of these waste streams and, in most cases, contract with used oil recyclers to remediate or dispose of the waste under the laws that regulate the transport, processing and destruction of the various components that make up these particular waste streams.
Currently, on-site remediation of these waste streams proves to be quite costly. The generators must contract with firms that have special expertise in reclaiming these waste streams as an on-site service. As an alternative, used oil recyclers can pick up oil from generators for transportation back to a plant for processing. After the oil is processed it can be resold as industrial burning fuel. This process of treating used oils is complex, costly and time consuming and produces waste components that require further remediation. Further, these used oils that are burned as fuel oils result in the original value of the oil being greatly reduced. Thorough purification to achieve a state as close to original quality and value as possible, much of the value of these recycled materials can be recovered. It has been the lack of an economical purification process of sufficient quality that has prevented the direct reuse or higher value use of these materials.
The use of supercritical fluids for separation and purification is known. A supercritical fluid is named based on the physical properties exploited. When a gas is compressed and maintained below its critical temperature, it becomes liquid. If during the compression the liquid gas is allowed to exceed its critical temperature, it will result into a dense gas called as supercritical fluid, whose pressure and temperature are above its critical states.
Supercritical fluids have solvation power similar to liquids, but also possess higher diffusion coefficients and lower viscosities at the same temperature. Supercritical fluids have the potential to extract components from a mixture at a more rapid extraction rate than possible with liquid extraction. The “gas like” low viscosities of supercritical fluids are 10-100 times lower than for liquids, and high diffusivities are 10-100 times higher than for liquids. The densities of supercritical fluids are 102 to 103 times greater than that of a gas at room temperature. Consequently the molecular interactions are greater due to shorter inter-molecular distances; hence the solvation power of supercritical fluids.
There are two general types of supercritical fluid systems typically employed for separation and purification. Both are fundamentally limited due to the specific technology and design approach. The first general type is a “batch” system, in which a batch is processed, the equipment is cleaned or serviced, another batch is processed, and the cycle is repeated as necessary. Batch systems operate at very high pressure and employ vessels of large volume; these systems are extremely expensive and inefficient. The second general type is a “continuous” system, in which the fluid to be processed is processed continuously, and not in “batches”. Existing continuous supercritical fluid systems utilize counter flow technology, in which feed material flows from top to bottom of a very complex long vertical column and a supercritical fluid flows from bottom to top of the column selectively dissolving specific components from the feed liquid. Systems of this type are very inefficient and rely on a large surface area on a wire mesh inside the column to strip off lighter components from the feed liquid. It requires many temperature sensors and complex controls, and it has very limited flow efficiency. Consequently, the liquid is usually required to be recycled several times to sufficiently extract desired components.
Various supercritical fluids have been used to facilitate the separation of emulsions. U.S. Pat. No. 5,435,920 to Penth discloses a process for cleaving spent emulsions such as cooling lubricants by means of carbon dioxide under pressure, and if necessary, heat in an economic and environmentally friendly manner. The emulsion of cooling lubricant is saturated under pressure with carbon dioxide and is heated and/or cooled until cleavage is achieved. Above the cleavage temperature, a floating water-poor oil phase quickly forms above an oil-poor aqueous phase. The process is not very efficient economically due to the relatively low solubility of lubricant in carbon dioxide.
Yamaguchi et al., Volumetric Behavior of Ethyl Esters Related to Fish Oil in the Presence of Supercritical CO2, the 4th International Symposium on Supercritical Fluids, May 11-14, Sendai Japan (1997), pp. 485-488, discloses using supercritical CO2 for the separation and fractionation of certain components of fish oil. The experimental apparatus included a static mixer in a water bath, and was a batch process. The batch process lowers the competitiveness of the process.
Another example of the use of supercritical CO2 is Nagase et al., Development of New Process of Purification and Concentration of Ethanol Solution using Supercritical Carbon Dioxide, Id. at pp. 617-619. The experimental apparatus included a pre-heater and a static mixer in an air bath.
Subramanian, M, Supercritical fluid extraction of oil sand bitumen from Uinta Basin, (Utah, Ph.D. dissertation, University of Utah, Salt lake city, Utah, 1996) discloses the use of propane to fractionate oil sand bitumen into different fractions. The process was not continuous in nature. U.S. Pat. No. 2,196,989 to Henry et al. discloses the use of propane in a batch process to purify used engine oil. U.S. Pat. No. 3,870,625 to Wielezynski discloses mixing propane and used oil in a column and letting gravity settle unwanted material in the bottom of the tank. A series of columns allows for multiple repetitions until propane is finally separated from the oil. U.S. Pat. No. 5,556,548 discloses a method by which liquid propane is mixed with used oil and propane/soluble oil is separated from sludge and heavy metal using a settling tank and gravity.
Notwithstanding advances in the art, the need still exists for a process for treating chemical fluids, particularly the recycling of oil, which can be used on-site, which utilizes a continuous flow system and that proves to be cost effective and environmentally friendly.